Para-xylene preparation using hydrogen scavenger



United States Patent 3,440,295 PARA-XYLENE PREPARATION USING HYDROGEN SCAVENGER Peter J. Capitano, East Orange, N.J., and Johannes W. Angelkorte, Montevallo, Ala., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 27, 1966, Ser. No. 604,562 Int. Cl. C07c /08 US. Cl. 260668 16 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved method for the preparation of p-xylylenes from p-xylene. More particularly, this invention relates to improving the efficiency of the pyrolysis of p-xylene in the preparations of pxylylenes therefrom.

A well known method of preparing p-xylylenes is to pyrolyze p-xylene, generally in the presence of inert diluent, to p-xylylene diradicals represented by the formula and thereafter condense the diradicals to p-xylylenes by known procedures. By the term p-xylylenes as used herein is meant those compositions containing the pxylylene unit ---0 Hz- C H in their structure, for example, cyclic di-p-xylylene and p-xylylene polymers.

The above pyrolyzation reaction, however, has been characterized by relatively low efficiency in that, typically less than 20 weight percent of the p-xylene is converted to the diradical due to hydrogen released in the course of the pyrolysis which causes side reactions, including dealkylation of p-xylene and other process inhibiting effects. It is therefore commercially desirable that released hydrogen be collected whereby process efficiency is much improved.

Accordingly, it is an object of the present invention to prepare p-xylylenes from p-xylene at improved process efficiency and yields.

It is another object of the present invention to improve the pyrolysis of p-xylene to p-xylylene diradical by introducing thereto hydrogen collecting additives or scavengers.

These and other objects are accomplished in the present invention wherein an improvement is provided in a method for preparing p-xylylenes by pyrolysis of p-xylene to p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes, the improvement which comprises contacting the p-xylene during pyrolysis with hydrogen collecting additives such as halogens, hydrocarbon ethers having 3 to having 1 to 12 carbon atoms, hydrocarbon aldehydes having 2 to 12 carbon atoms, ketones having 2 to 12 carbon atoms, ketenes having 3 to 8 carbon atoms, anhydrides having 2 to 24 carbon atoms, carboxylic acids 24 carbon atoms, organic halides 7 "ice having 2 to 24 carbon atoms, sulfur, alkyl sulfides having 1 to 10 carbon atoms, alkyl sulfoxides having 1 to 10 carbon atoms, alkyl sulfones having 1 to 10 carbon atoms, mercaptans having 1 to 20 carbon atoms or nitroparafiins having 1 to 10 carbon atoms.

Typically p-xylene is pyrolyzed in the presence of a suitably inert diluent such as steam at between about 800 C. and 1000 C. to form p-xylylene diradicals which can then be condensed to p-xylylenes such as cyclic dip-xylylene or poly-p-xylylene by known methods; see, for example, US. Patent 2,149,175 to D. F. Pollart which is herein incorporated by reference.

Although other inert diluents can be employed in the pyrolysis of p-xylene, such as nitrogen, steam is generally employed as indicated above. The amount of steam present in this process is not narrowly critical but it is preferably employed in an amount of at least about 50 moles per mole of p-xylene and generally between about to 200 moles per mole of p-xylene although excess steam is not detrimental to the process.

It has been found that the addition of selected additives in the pyrolysis of p-xylene has considerably improved the yield therefrom of p-xylylenes including polyp-xylylene and di-p-xylylene. The additives, which are described below, are those which under pyrolysis conditions dissociate into free radicals or reactive intermediates and act as hydrogen scavengers to enhance the formation of the p-xylylene diradical.

The additives can be introduced directly to the pyrolysis zone, added to the p-xylene or to the diluent therefor. For example, as gases or liquids, the additive or additives can be premixed with the p-xylene or the diluent or metered directly into the pyrolysis zone if practical. If a solid, the additive can be dissolved either in a suitable solvent and added as a liquid above or, if feasible, dissolved in the diluent or the p-xylene itself.

Pyrolysis of the p-xylene is conveniently conducted by vaporizing the p-xylene and passing it through a pyrolysis zone preferably a heated tube or reaction vessel for a short period of time. Time of contact in the pyrolysis zone must be at least sufficient to pyrolyze or crack a portion of the p-xylene into the reactive diradical, p xylylene, but not so long that charring or complete decomposition occurs. Contact time depends to a great degree on the particular temperature selected for pyrolysis; the lower the temperature the longer the permissible contact time and vice versa. At most desirable conditions of about 900 C. contact times are preferably between about 0.03 to 0.50 second. Seldom would it be desirable to have a contact time greater than one second. At the higher operating temperatures, contact times of 0.01 second or shorter may at times be indicated.

The additives of the present invention which may be added to the pyrolysis of p-xylene singly or severally are listed below.

The halogen additives of the invention include chlorine, bromine and the like. Suitably, a 1.0/1 to 6.3/1 mole ratio of p-xylene to halogen is employed. It will be recognized that greater or lesser proportions of these additives than the given mole ratios indicate, including those additives listed hereinafter, can be added if desired within the scope of the present invention.

The hydrocarbon ether additives can contain from 3 to 24 carbon atoms and inculde saturated aliphatic hydrocarbon ethers such as methyl ethyl ether, diethyl ether and dipropyl ether; unsaturated aliphatic hydrocarbon ethers such as vinyl ethyl ether; aromatic hydrocarbon ethers including the aryl ethers and alkaryl ethers such as phenetole and anisole and cycloaliphatic hydrocarbon ethers including 1,4-dioxane, tetrahydrofuran and the epoxides such as ethylene oxide, trimethylene oxide,

3 the like. Suitably, a 5/1 to 13/1 mole ratio of p-xylene to ether is employed.

The organic halide additives can contain from 1 to 12 carbon atoms and include saturated aliphatic halides such as methyl chloirde, ethyl chloride, methyl bromide, ethyl bromide and the like. Suitably a 1/ 1 to 6/1 mole ratio of p-xylene to alkyl halide is employed.

The organic halide additives also include saturated aliphatic polyhalides including the alkene halide additives such as methylene halides including methylene chloride, methylene bromide; ethylene halides such as ethylene chloride; polyalkene halides such as trimethylene bromide and the like as well as the trihalo alkane additives such as bromoform, iodoform and the like and the tetrahalo alkanes such as carbon tetrachloride and the like. Suitably, a 3/1 to 9/1 mole ratio of p-xylene to alkene halide is employed except for the trihalo alkanes where a 9/1 to 12/1 mole ratio is employed and the tetrahalo alkanes where a 1/1 to 10/1 mole ratio is employed.

The organic halide additives further include unsaturated aliphatic halides such as allyl halides including l-chloro- 3-propene and the like; methallyl halides such as 4- bromo-l-butene and thel ike.

The hydrocarbon aldehyde additives include the aliphatic aldehydes having from 2 to 12 carbon atoms such as acetaldehyde, propionaldehyde and the like as Well as the aromatic aldehydes such as benzaldehyde, p-tolyaldehyde and the like. Suitably a 2/1 to 10/1 mole ratio of p-xylene to aldehyde is employed.

The hydrocarbon ketone additives include those additives having one or more carbonyl groups and having from 2 to 12 carbon atoms such as the aliphatic ketones including acetone, 2-propanone, 2-butyrone, acetylacetone, biacetyl and the like; the aromatic ketones such as acetophenone, n-butyrophenone and the like and cyclic ketones such as tetramethyl-1,3-cyclobutanedione, 1,4-cyclohexanedion and the like. Suitably a 4/1 to 15/1 mole ratio of p-xylene to ketone is employed.

The ketene additives include ketene and diketene. Suitably a 5/1 to 40/1 mole ratio of p-xylene to ketene is employed.

The anhydride additives include aliphatic anhydrides having from 2 to 24 carbon atoms such as acetic anhydride, propionic anhydride, n-butyric anhydride, n-valeric anhydride, n-caproic anhydride and the like. Suitably a 10/1 to 40/ 1 mole ratio of p-xylene to anhydride is employed.

The carboxylic acid additives include those additives having one or more carboxylic acid groups and containing from 2 to 24 carbon atoms such as the aliphatic carboxylic acids including acetic acid, propionic acid, butyric acid and the like, and oxalic acid, malonic acid, succinic acid and the like, as well as aromatic carboxylic acids such as benzoic acid, phthalic acid, naphthalic acid and the like and the aromatic aliphatic carboxylic acids such as phenyl acetic acid and the like. Suitably a 5/1 to 1 mole ratio of p-xylene to carboxylic acid is employed.

The sulfur additives include sulfur itself, hydrocarbon sulfur additives including alkyl sulfides having 1 to 10 carbon atoms such as dimethyl sulfide, dimethyl disulfide, diethyl sulfide and the like; alkyl sulfoxides such as dimethyl sulfoxide; alkyl sulfones such as dimethyl sulfone and hydrocarbon mercaptans having 1 to 10 carbon atoms, such as methanethiol, ethanethiol, l-propanethiol and aryl mercaptans such as benzenethiol, a,oz'dimercapto p-xylene and the like. Suitably a 10/1 to 40/1 mole ratio of p-xylene to sulfur additive is employed.

The nitroparaflin additives have 1 to 10 carbon atoms and include nitromethane, nitroethane and the like. Suitably a 10/1 to 20/1 mole ratio of p-Xylene to nitroparafiin is employed.

The above additives are employed with a contact time of preferably between .01 to .10 second at temperatures between 800 C. and 1000" C.

The following examples are intended as illustrations of the invention and should not be construed in limitation thereof. All parts and percentages given are by weight unless otherwise specified.

EXAMPLE I (a) Non-additive run A mixture of distilled water and p-xylene vapors was fed into a 1 x 12 in. pyrolysis tube maintained at 900 C. and atmospheric pressure at such a rate as to give a contact time in the pyrolysis zone of 0.056 second and a p-xylene partial pressure of 6.44 mm. Hg. The pyrolysate vapors were transferred through an insulated delivery tube into a flask containing, as a quench bath, a refluxing azeotrope mixture of diethylbenzene and water.

' The run continued for a period of four hours during which grams of p-xylene and 2000 grams of distilled water were passed through the pyrolysis system. Water was removed from the quench bath as soon as it collected as a separate phase. At the end of the run, the diethylbenzene solution was collected, filtered, dried over anhydrous M SO and reduced to 1/10 its original volume by distillation at reduced pressure (20 mm). The concentrated solution was allowed to cool to room temperature (25 C.) at which point about 2.60 grams of di-p-xylyene with a M.P. of 283-285 C. crystallized therefrom and was recovered by filtration. An additional 5.60 grams of poly-p-xylene was recovered from the walls of the flask housing the quench bath, which when combined with the di-p-xylene afforded a total yield of 7.70% for this standard or non-additive run.

(b) Acetic acid additive run A mixture of distilled water, glacial acetic acid, and p-xylene vapors was fed into a 1 x 12 in. pyrolysis tube maintained at 900 C. and atmospheric pressure at such a rate as to give a contact time of 0.050 second in the pyrolysis zone and p-xylene partial pressure of 3.50 mm. The glacial acetic acid was combined with the distilled water feed in a sufficient amount to provide a p-xyleneacetic acid mole ratio of 10 to l.

The run was conducted in the manner of Example 1(a) and continued for four hours during which time 100 grams of pxylene, 5.5 gms. of glacial acetic acid and 4000 grams of distilled Water were passed through the pyrolysis unit. Thereafter about 7.40 grams of crystalline di-para-xylylene with a M.P. of 283-285 C. and 7.70 grams of poly-para-xylylene were recovered afiording a total yield of 15.10% for the acetic acid additive run.

EXAMPLE II (a) Non-additive run A mixture of distilled water and p-xylene vapors was fed into a l x 12 in. pyrolysis tube maintained at 900 C. and atmospheric pressure at such a rate as to give a contact time in the pyrolysis zone of 0.045 second with a pxylene partial pressure of 3.40 mm. The pyrolysate vapors were transferred by means of an insulated delivery tube into a flask containing a refluxing mixture of diethyl benzene-water azeotrope as a quench bath.

The run continued for a period of four hours during which time a total of 100 grams of p-xylene and 4000 grams of distilled water were passed through the pyrolysis unit. Water was removed as it collected in a separate phase in the quench bath. At the end of the run, the diethylbenzene solution was collected, filtered, dried over anhydrous M SO and concentrated by distillation under reduced pressure (20 mm.) to its original volume. The concentrated solution was allowed to cool to room temperature (25 C.) at which point 3.10 grams of di-paraxyl-ylene melting at 283285 C. crystallized from solution and was recovered. An additional 2.90 grams of polypara-xylylene was recovered from the walls of the flask housing the quench bath aflording, when combined with propylene oxide, 1,3 epoxy butane, wu-epoxybibenzyl and the recovered di-para-xylylene, a total of 6.00% yield for the non-additive or standard run.

(b) Acetic anhydride additive run A mixture of distilled water, acetic anhydride, and pxylene vapors were fed into a 1 x 12 in. pyrolysis tube at such a rate as to give a contact time of 0.047 second in the pyrolysis zone and a p-xylene partial pressure of 3.40 mm. The acetic anhydride was combined with the distilled water feed in a suflicient amount as to provide a p-xylene-acetic anhydride mole ratio of 10 to 1. The run was conducted and worked up in the manner of Example II(a) and continued for four hours during which time 100 grams of p-xylene, 9.6 grams of acetic anhydride and 4000 grams of distilled water were passed through the pyrolysis unit. Thereafter about 5.30 grams of crystalline di-para-xylylene with a M.P. of 283-285 C. and 7.20 grams of poly-para-xylylene were recovered affording, when combined, a total of 12.50% yield for the acetic anhydride additive run.

Further examples were conducted with several of the additives discussed above being employed in the pyrolysis of p-xylene (PX) as illustrated in Tables I, II and III. In Tables I and II the weight percent of di-p-xylylene (DPX) recovered (DPX Weight divided by input PX Weight multiplied by 100) is recorded while in Table III the recovery of the weight percent of di-p-xylene and poly-p-xylene (PPX) is listed. The temperature of the runs was between 850 to 900 C. and the additive contact times were between .045 and .050 second except for dimethyl sulfide, which was employed with a contact time of .080 second.

TABLE I Wt. percent Input mole DPX Increase, Additive ratio PX/ recovered percent additive (DPXIPX DPX input) Non-additive 2. 7 Chlorine 6. 3 4. 3 59. 3 Ethylene oxide- 12. 7 4. 6 70.3 Methyl bromide. 2. 7 5. 4 100. Methylene bromi 8. 6 5. 0 85. 2 Methyl chloride 2. 4 4.1 51. 9 Methylene chloride 3. 2 6. 5 141. 8 Chloroform 10. 1 4. 6 70.3 D methyl sulfide 20.0 4. 6 70. 3 Diethyl ether 10.0 4. 4 63.0 Nitromethane. 20. 0 4. 8 77. 8

TAB LE II Wt. percent Input mole D PX Increase, Additive ratio PX] recovered percent additive (DPXIPX DPX input) Nonadditive 1. 0 Carbon tetrachloride. 2. 5 2. 6 160. 0 1 chlortrB-propene 20.0 3. 9 290. 0 Acetaldehyde 10. 0 1. 2 20. 0 Diketene 20. 0 2. 8 180.0 Acetone 5. 0 4. 2 320. 0

TABLE III Wt. percent Input mole DPX+PPX Percent Additive ratio PX (DPX+ 1 nor-ease to additive PIX/PX DPX+PPX input) Non-additive 6. 0 Acetic anhydride- 12.5 108.5 a,a-Dimercapto p-Xylene 12. 1 103 0 Non-additive 7. 7 Acetic acid 15. 1 96. 2

Thus it is readily apparent that the addition of small amounts of the additives of the invention markedly increase the yield of the p-xylylene diradicals as evidenced by the increased production of di-p-xylylene and poly-pxylylene.

What is claimed is:

1. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes, the improvement which comprises contacting the p-xylene during said pyrolysis with a hydrogen scavenger selected from the group consisting of halogens, hydrocarbon ethers having 3 to 24 carbon atoms, organic halides having 1 to 12 carbon atoms, hydrocarbon aldehydes having 2 to 12 carbon atoms, hydrocarbon ketones having 2 to 12 carbon atoms, ketenes having 3 to 8 carbon atoms, anhydrides having 2 to 24 carbon atoms, carboxylic acids having 2 to 24 carbon atoms, sulfur, alkyl sulfides having 1 to 10 carbon atoms, alkyl sulfoxides having 1 to 10 carbon atoms, alkyl sulfones having 1 to 10 carbon atoms, hydrocarbon mercaptans having 1 to 10 carbon atoms and nitroparaifins having 1 to 10 carbon atoms whereby the conversion efiiciency and yield of p-xylylenes is increased.

2. The method of claim 1 wherein said p-xylylene is pyrolyzed from .01 to .10 second.

3. The method of claim 1 wherein p-xylene is pyrloyzed at temperatures between 800 C. and 1000 C.

4. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a halogen as a hydrogen scavenger.

5. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a hydrocarbon ether having 3 to 24 carbon atoms.

6. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with an alkyl halide having 1 to 12 carbon atoms.

7. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a hydrocarbon aldehyde having 2 to 24 carbon atoms.

8. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said pxylylenes the improvement comprising contacting pxylene during said pyrolysis with a hydrocarbon ketone having 2 to 12 carbon atoms.

9. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a ketene having 3 to 8 carbon atoms.

10. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-Xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with an anhydride having 2 to 24 carbon atoms.

11. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a carboxylic acid having 2 to 12 carbon atoms.

12. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a sulfur as a hydrogen scavenger.

13. In a method for preparing p-xylylenes comprising pyrolysis of p-xyleue generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-Xylene during said pyrolysis with an alkyl sulfide having 1 to 10 carbon atoms.

14. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a hydrocarbyloxy sulfur additive having 1 to 10 carbon atoms.

15. In a method for preparing p-xylylenes comprising pyrolysis of p-Xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes the improvement comprising contacting p-xylene during said pyrolysis with a hydrocarbon mercaptan having 1 to 10 carbon atoms.

16. In a method for preparing p-xylylenes comprising pyrolysis of p-xylene generating p-xylylene diradicals and thereafter condensing said diradicals to said p-xylylenes References Cited UNITED STATES PATENTS 3,149,175 9/1964 Pollart 260670 3,247,274 4/1966 Pollart 260670 3,271,471 9/1966 Baker 260670 3,274,127 9/1966 SWarc 2602 3,110,745 11/1963 Peck et a1 260672 3,178,485 4/1965 Myers 260672 DELBERT E. GANTZ, Primary Examiner.

' G. E. SCHMITKONS, Assistant Examiner.

US. Cl. X.R. 2602, 670 

